Optimum Tilt Angle of Flow Guide in Steam Turbine Exhaust Hood Considering the Effect of Last Stage Flow Field

2017 ◽  
Vol 30 (4) ◽  
pp. 866-875 ◽  
Author(s):  
Lihua CAO ◽  
Aqiang LIN ◽  
Yong LI ◽  
Bin XIAO
Keyword(s):  
Flow Field ◽  
Steam Turbine ◽  
Tilt Angle ◽  
Exhaust Hood ◽  
Last Stage ◽  
Flow Guide ◽  
Turbine Exhaust

Influence of a Cylindrical Exhaust Hood Installation on the Last Stage Rotor Blades of a Low Pressure Model Steam Turbine

2017 ◽  
Author(s):  
Fabian F. Müller ◽  
Markus Schatz ◽  
Damian M. Vogt ◽  
Jens Aschenbruck
Keyword(s):  
Flow Field ◽  
Steam Turbine ◽  
Operating Conditions ◽  
Rotor Blades ◽  
Pressure Measurements ◽  
Exhaust Hood ◽  
Blade Vibration ◽  
Time Resolved ◽  
Vibration Behavior ◽  
Last Stage

The influence of a cylindrical strut shortly downstream of the bladerow on the vibration behavior of the last stage rotor blades of a single stage LP model steam turbine was investigated in the present study. Steam turbine retrofits often result in an increase of turbine size, aiming for more power and higher efficiency. As the existing LP steam turbine exhaust hoods are generally not modified, the last stage rotor blades frequently move closer to installations within the exhaust hood. To capture the influence of such an installation on the flow field characteristics, extensive flow field measurements using pneumatic probes were conducted at the turbine outlet plane. In addition, time-resolved pressure measurements along the casing contour of the diffuser and on the surface of the cylinder were made, aiming for the identification of pressure fluctuations induced by the flow around the installation. Blade vibration behavior was measured at three different operating conditions by means of a tip timing system. Despite the considerable changes in the flow field and its frequency content, no significant impact on blade vibration amplitudes were observed for the investigated case and considered operating conditions. Nevertheless, time-resolved pressure measurements suggest that notable pressure oscillations induced by the vortex shedding can reach the upstream bladerow.

Numerical Investigation of the Influence of Flow Deflection at the Upper Hood on Performance of Low Pressure Steam Turbine Exhaust Hoods

2019 ◽  
Author(s):  
Dickson Munyoki ◽  
Markus Schatz ◽  
Damian M. Vogt
Keyword(s):  
Mach Number ◽  
Steam Turbine ◽  
Swirling Flows ◽  
Steam Turbines ◽  
Exhaust Hood ◽  
Design Load ◽  
Last Stage ◽  
Flow Deflection ◽  
Turbine Exhaust ◽  
Loss Mechanisms

Abstract Most of the world’s power is produced by large steam turbines using fossil fuel, nuclear and geothermal energy. The LP exhaust hoods of these turbines are known to contribute significantly to the losses within the turbine, hence a minor improvement in their performance, which results in a lower backpressure and thus higher enthalpy drop for the steam turbine, will give a considerable benefit in terms of fuel efficiency. Understanding the flow field and the loss mechanisms within the exhaust hood of LP steam turbines is key to developing better optimized exhaust hood systems. A detailed analysis of loss generation within the exhaust hood was done by the authors [1]. It was found that most losses occur at the upper hood and are caused by the swirling flows, which mostly start at the diffuser outlet, especially for the top diffuser inlet sector flows that have a complex path to the condenser. The authors further numerically investigated the influence of hood height variation on performance of an LP turbine exhaust hood [2], which further contributed to the knowledge of the loss mechanisms. With the loss mechanisms in exhaust hoods reasonably well understood, flow deflection at the upper hood is investigated in the current paper. The deflection is aimed at minimizing the intensity of the vortices formed thus reducing the exhaust losses. The deflector configurations analyzed are modifications of the walls of the reference configuration’s outer casing. The numerical models of the reference configuration which are based on a scaled axial-radial diffuser test rig operated by ITSM have already been validated by the authors at design and overload operating conditions and three tip jet Mach numbers (0, 0.4 and 1.2)[1]. Deflector configurations investigated are found to re-direct the flow at the upper hood and minimize the intensity of the swirling flows hence leading to improvement in performance of LP steam turbine exhaust hoods. The best performing deflector configuration is found to give a considerable improvement in performance of 20% at design load and 40% at overload both at tip jet Mach number of 0.4 (corresponding to shrouded last stage blades). At design load and tip jet Mach number of 1.2 (corresponding to unshrouded last stage blades), the improvement is found to be moderate. About 7% performance increase is observed.

Study of Coupling Numerical Flow Field Simulation of Low-Pressure Last Stage Exhaust Passage in Steam Turbine

2014 ◽  
Vol 672-674 ◽  
pp. 1626-1632
Author(s):  
Zhen Song ◽  
Jian Qun Xu ◽  
Li Peng Sun ◽  
Ming Tao Liu
Keyword(s):  
Flow Field ◽  
Steam Turbine ◽  
Turbulence Model ◽  
Pressure Loss ◽  
Total Pressure ◽  
Exhaust Hood ◽  
Coupled Models ◽  
Field Simulation ◽  
Inlet Swirl ◽  
Last Stage

The model of coupled exhaust hood with condenser throat and the model of coupled exhaust hood, condenser throat with last stage were simulated based on the turbulence model Realizable k-ε. Calculated results show that due to the ignoring of the inlet swirl in the model coupled exhaust hood with condenser throat, the flow field is symmetrical and the pressure loss is small. Due to the influence of last stage, in the model of coupled exhaust hood, condenser throat with last stage, the flow field of the inlet of the exhaust hood is uneven, and the vortexes changed more complex, resulting in the increase of the pressure loss of each part and a greater influence in the diffuser pipe. The proportion of pressure loss of diffuser pipe in total pressure loss increases from 0.086 to 0.358, and there is a 70% decline of proportion of pressure loss in volute and condenser throat. In addition, the proportion of the pressure loss in volute is the largest one in these two coupled models. So more attention should be paid in the influence of the last stage, and weaken the vortexes in the volute when designing or optimizing the exhaust passage of steam turbine.

Experimental and Numerical Investigations of Steam Turbine Exhaust Hood Flow Field With Two Types of Diffusers

2019 ◽  
Author(s):  
Soichiro Tabata ◽  
Hisataka Fukushima ◽  
Kiyoshi Segawa ◽  
Koji Ishibashi ◽  
Yoshihiro Kuwamura ◽  
...  
Keyword(s):  
Flow Field ◽  
Flow Pattern ◽  
Steam Turbine ◽  
Three Dimensional ◽  
Internal Flow ◽  
Exhaust Hood ◽  
Scaled Model ◽  
Last Stage ◽  
Verification Test ◽  
Lp Turbine

Abstract The exhaust hood performance of LP turbine plays an important role in the efficiency of steam turbine. By improving the exhaust performance, the kinetic energy of the last stage rotating blades can be converted to the potential energy and it becomes possible to improve the turbine efficiency. However, the flow field in the diffuser is closely related to the flow pattern of the last stage rotating blade, and the flow field inside the exhaust chamber afterward has a complicated three dimensional flow field. Therefore, in this study, it conducted a scaled model steam turbine test using two types of diffusers and CFD, and evaluated exhaust performance and flow pattern. The verification test was carried out using a test turbine (4 stages) of × 0.33 scale, the velocity field and the pressure field were evaluated by traverse and the wall pressure measurements. The corresponding CFD was calculated by ANSYS CFX. All four stages of blades and seals, exhaust chambers were accurately modeled. Due to the detailed CFD, the internal flow of the exhaust chamber exhibiting complicated three-dimensionality was visualized and the flow pattern was evaluated. The verification test results and the corresponding CFD results were compared and evaluated, and it has been found that the overall performance predicted by CFD is well showing the verification test result. Therefore, it has been found that CFD can help to understand the internal flow of the exhaust chamber exhibiting complex three-dimensional characteristics.

Numerical Investigation on the Aerodynamic Performance of a Low-Pressure Steam Turbine Exhaust Hood Using Design of Experiment Analysis

2020 ◽  
Vol 142 (11) ◽  
Author(s):  
Tommaso Diurno ◽  
Tommaso Fondelli ◽  
Leonardo Nettis ◽  
Nicola Maceli ◽  
Lorenzo Arcangeli ◽  
...  
Keyword(s):  
Flow Field ◽  
Steam Turbine ◽  
Design Of Experiment ◽  
Low Pressure ◽  
Pressure Recovery ◽  
Exhaust Hood ◽  
Recovery Coefficient ◽  
Pressure Steam ◽  
Pressure Recovery Coefficient ◽  
Turbine Exhaust

Abstract Nowadays, the rising interest in using renewable energy for thermal power generation has led to radical changes in steam turbine design practice and operability. Modern steam turbines are required to operate with greater flexibility due to rapid load changes, fast start-up, and frequent shutdowns. This has given rise to great challenges to the exhaust hood system design, which has a great influence on the overall turbine performance converting the kinetic energy leaving the last stage of low-pressure turbine into static pressure. The radial hoods are characterized by a complex aerodynamic behavior since the flow turns by 90 deg in a very short distance and this generates a highly rotational flow structure within the diffuser and exhaust hood outer casing, moreover, the adverse pressure gradient can promote the flow separation drastically reducing the hood recovery performance. For these reasons, it is fundamental to design the exhaust system in order to ensure a good pressure recovery under all the machine operating conditions. This paper presents a design of experiment (DOE) analysis on a low-pressure steam turbine exhaust hood through computational fluid dynamics (CFD) simulations. A parametric model of an axial-radial exhaust hood was developed, and a sensitivity of exhaust hood performance as a function of key geometrical parameters was carried out, with the aim of optimizing the pressure recovery coefficient and minimizing the overall dimensions of the exhaust casing. Since hood performance strongly depends on a proper coupling with the turbine rear stage, such a stage was modeled using the so-called mixing-plane approach to couple both stator–rotor and rotor-diffuser interfaces. A detailed analysis of the flow field in the exhaust hood in the different configurations was performed, detecting the swirling structures responsible for the energy dissipation in each simulation, as well as correlating the flow field with the pressure recovery coefficient.

Efficient Methods for Predicting Low Pressure Steam Turbine Exhaust Hood and Diffuser Flows at Design and Off-Design Conditions

2015 ◽  
Vol 137 (8) ◽  
Author(s):  
Zoe Burton ◽  
Grant Ingram ◽  
Simon Hogg
Keyword(s):  
Steam Turbine ◽  
Static Pressure ◽  
Pressure Recovery ◽  
Exhaust Hood ◽  
Current Standard ◽  
Industrial Practice ◽  
Flow Asymmetry ◽  
Pressure Steam ◽  
Last Stage ◽  
Turbine Exhaust

The exhaust hood of a steam turbine is an important area of turbomachinery research as its performance strongly influences the power output of the last stage blades (LSB). This paper compares results from 3D simulations using a novel application of the nonlinear harmonic (NLH) method with more computationally demanding predictions obtained using frozen rotor techniques. Accurate simulation of exhausts is only achieved when simulations of LSB are coupled to the exhaust hood to capture the strong interaction. One such method is the NLH method. In this paper, the NLH approach is compared against the current standard for capturing the inlet circumferential asymmetry, the frozen rotor approach. The NLH method is shown to predict a similar exhaust hood static pressure recovery and flow asymmetry compared with the frozen rotor approach using less than half the memory requirement of a full annulus calculation. A second option for reducing the computational demand of the full annulus frozen rotor method is explored where a single stator passage is modeled coupled to the full annulus rotor by a mixing plane. Provided the stage is choked, this was shown to produce very similar results to the full annulus frozen rotor approach but with a computational demand similar to that of the NLH method. In terms of industrial practice, the results show that for a typical well designed exhaust hood at nominal load conditions, the pressure recovery predicted by all methods (including those which do not account for circumferential uniformities) is similar. However, this is not the case at off-design conditions where more complex interfacing methods are required to capture circumferential asymmetry.

Aerodynamics Prediction and Design of a Steam Turbine Exhaust Hood

2014 ◽  
Author(s):  
Daiwei Zhou ◽  
Bo Liu ◽  
Xiaocheng Zhu ◽  
Zhaohui Du
Keyword(s):  
Optimal Design ◽  
Flow Field ◽  
Steam Turbine ◽  
Experimental Measurement ◽  
Low Pressure ◽  
Pressure Recovery ◽  
Exhaust Hood ◽  
Optimization System ◽  
Operation Conditions ◽  
Turbine Exhaust

The exhaust hood of a low pressure steam turbine is a component that has the potential to be improved considerably in terms of aerodynamic efficiency. In the present study, flow structures in the exhaust hood model of the low pressure stream turbine are investigated with experimental measurement and numerical simulation. The flow field in a modern type of exhaust hood is illustrated. The flow field predicted by CFD is validated by experimental measurement. Then, this paper introduces an aerodynamic optimization system to further improve the pressure recovery capability of low pressure turbine exhaust hood. The optimization system is developed with the Kriging surrogate model and the CFD method. The aerodynamic benefit provided by the optimal exhaust hood is explained. Finally, to scrutinize the static pressure recovery capability of the optimized exhaust hood, a full-scale exhaust hood coupled with last three stages is used to numerically evaluate the optimal design at four different flow rates. It is demonstrated that the optimal design from the air model can be used in the actual exhaust hood in different operation conditions.

Numerical Investigation and Validation of the 1 090 MW Steam Turbine Exhaust Hood Flow Field

2017 ◽  
Author(s):  
A. Živný ◽  
A. Macálka ◽  
M. Hoznedl ◽  
K. Sedlák ◽  
M. Hajšman ◽  
...  
Keyword(s):  
Flow Field ◽  
Steam Turbine ◽  
Nuclear Power ◽  
Flow Behavior ◽  
Three Dimensional ◽  
Exhaust Hood ◽  
Recovery Coefficient ◽  
Strongly Coupled ◽  
Lp Turbine ◽  
Turbine Exhaust

The last-stage blade (LSB) rows and exhaust hood in low-pressure (LP) steam turbine sections are key elements of the entire LP turbine part. The cold end section affects significantly the whole LP turbine efficiency and overall turbine performance due to huge steam expansion. This expansion is strongly coupled with the diffuser and exhaust hood, which transforms kinetic energy at the stage exit into potential energy. Mentioned mechanism leads to expansion line prolongation between the stage inlet and diffuser outlet and higher turbine power output. An experimental investigation of the flow field in the exhaust hood is very economically and procedurally expensive and not commonly feasible. Nowadays, capable numerical simulations can provide relatively fast and accurate results on any studied model. On the other hand, the flow behavior inside the LSB and the exhaust hood is very complex and it is still challenging to investigate the whole system using CFD codes. The purpose of this paper is to validate complex three-dimensional CFD methodology of the flow field in the operating 1 090 MW steam turbine exhaust hood with radial diffuser and condenser neck. The exceptional contribution of this paper is the fact that unique data obtained by measurement on operating Nuclear Power Plant (NPP) steam turbine are available. The comparison is focused mainly on the pressure, velocity and steam wetness distribution along the LSB height at the stage exit/diffuser inlet. Wall static pressures and the pressure recovery coefficient of the exhaust hood were also determined and compared with experimental data. The complete CFD study helps to understand the flow behavior inside the whole exhaust throat and locate critical parts that negatively affect aerodynamic design.

Numerical Investigation on the Aerodynamic Performance of a Low-Pressure Steam Turbine Exhaust Hood Using DOE Analysis

2020 ◽  
Author(s):  
Tommaso Diurno ◽  
Tommaso Fondelli ◽  
Leonardo Nettis ◽  
Nicola Maceli ◽  
Lorenzo Arcangeli ◽  
...  
Keyword(s):  
Flow Field ◽  
Steam Turbine ◽  
Low Pressure ◽  
Operating Conditions ◽  
Pressure Recovery ◽  
Exhaust Hood ◽  
Recovery Coefficient ◽  
Pressure Steam ◽  
Pressure Recovery Coefficient ◽  
Turbine Exhaust

Abstract Nowadays, the rising interest in using renewable energy for thermal power generation has led to radical changes in steam turbine design practice and operability. Modern steam turbines are required to operate with greater flexibility due to rapid load changes, fast start-up, and frequent shutdowns. This has given rise to great challenges to the exhaust hood system design, which has a great influence on the overall turbine performance converting the kinetic energy leaving the last stage of LP turbine into static pressure. The radial hoods are characterized by a complex aerodynamic behavior since the flow turns by 90° in a very short distance and this generates a highly rotational flow structure within the diffuser and exhaust hood outer casing, moreover, the adverse pressure gradient can promote the flow separation drastically reducing the hood recovery performance. For these reasons it is fundamental to design the exhaust system in order to ensure a good pressure recovery under all the machine operating conditions. This paper presents a Design of Experiment analysis on a low-pressure steam turbine exhaust hood through CFD simulations. A parametric model of an axial-radial exhaust hood was developed and a sensitivity of exhaust hood performance as a function of key geometrical parameters was carried out, with the aim of optimizing the pressure recovery coefficient and minimizing the overall dimensions of the exhaust casing. Since hood performance strongly depends on a proper coupling with the turbine rear stage, such a stage was modeled using the so-called mixing-plane approach to couple both stator-rotor and rotor-diffuser interfaces. A detailed analysis of the flow field in the exhaust hood in the different configurations was performed, detecting the swirling structures responsible for the energy dissipation in each simulation, as well as correlating the flow field with the pressure recovery coefficient.

A Comparison of Two Methods for Utilizing Steam Turbine Exhaust Hood Flow Field Data

1992 ◽  
Vol 114 (2) ◽  
pp. 398-401 ◽  
Author(s):  
R. H. Tindell ◽  
T. M. Alston
Keyword(s):  
Flow Field ◽  
Steam Turbine ◽  
Three Dimensional ◽  
Internal Flow ◽  
Loss Coefficient ◽  
Navier Stokes ◽  
Exhaust Hood ◽  
Flow Properties ◽  
Very High ◽  
Turbine Exhaust

This article describes the effects of two methods for representing the nonuniform distribution of flow properties across a steam turbine discharge annulus, on the hood loss coefficient. One method uses a mass-weighted integration of the property across the station, while the other is based on a mass-derived representative value of the property. The former has the potential for very high accuracy provided a sufficient number of points are integrated. The latter, while less accurate, is easier to apply and therefore more commonly used. The analytical modeling includes a simplistic step profile of pressure across the annulus, as well as a three-dimensional exhaust hood, flow-field simulation calculated using a Navier–Stokes code. Results show that significant errors can occur in the hood loss coefficient with the mass-derived approach. Although the analysis centers on hood loss coefficient as the performance parameter whose sensitivity is being monitored, the results highlight the pitfalls of improper application of measured data for any internal flow system.

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